1. FIELD OF THE INVENTION
This invention relates to telephone paystations and more particularly to a paystation modification that prevents users from fraudulent use of the telephone instrument.
2. DESCRIPTION OF THE BACKGROUND ART
When the Model 120B paystation telephone, as manufactured by Palco Telecom Inc., is utilized in those locations where connections are made to a digital telephone central office, it is desirable to provide modification for the paystation circuitry to prevent users from fraudulent use of the telephone instrument by means of a short disconnect signal thus returning to the "off-hook" condition before or during coin battery operation. When this condition takes place, the telephone instrument will remain in a state where the user may be required to deposit only a single coin (as small as a five cent piece) to condition the instrument for proper usage. This situation takes place usually in digital offices and is not found in most older analog offices because of the nature of the techniques employed in such offices where they detect "on-hook" and "off-hook" conditions and the speed in which they connect and remove coin battery signals.
Paystations that are designed to work in the emergency prepay mode do not require the usual coin deposit to enable the calling device (dial or tone keypad). This arrangement is created so that users may call emergency numbers (911, etc.) without making coin deposits. If the user dials a number other than an emergency number designated by the central office, the office then will perform a coin test to determine if the initial rate of coins have been deposited. This test then looks for the presence of ground current or a difference in current through the two loop conductors. When the initial rate has been deposited the paystation connects a load, usually the coin relay circuit, to earth ground. This load then provides the necessary current path back to the central office to indicate the presence of the initial coin deposit has been made.
In the prepay mode of operation, deposit of coins up to the initial rate is typically required before the calling device is enabled. Also, when the initial rate has been deposited the paystation is conditioned to connect a load to ground to signal the telephone central office that indeed the initial rate has been deposited.
After the call is terminated, the paystation condition is then set to enable the collect or refund of any coins that have been deposited. When the telephone paystation first goes off-hook the paystation is set to that condition where no coins have been deposited, the ground path that indicates that the initial rate deposit has been made is removed.
In the aforementioned 120B paystation, a condition exists where that ground path to the coin relay is not cleared and the telephone remains in the prepay mode with the calling device not disabled. Thus, under such conditions, all that is required is the deposit of a single coin to make the mechanical switch in the coin relay close, thus establishing the ground path to satisfy the central office requirement.